Ultrasonic medical transducers are used to observe the internal organs of a patient. Such an apparatus produces the display of successive images at a rapid rate so that an observer can see movements of an organ in "real time." Ultrasonic transducer assemblies are manufactured in a number of configurations including curved arrays, linear arrays, and non-array transducers such as doppler and concentric transducers, to name a few. The type of configuration of transducer used for a given application depends upon the type of medical observation to be performed. By way of example, a curved array transducer produces an image over a wider field of view and thus permits the observer to view objects that would ordinarily be hidden from view when using a linear array. For example a bone, such as a rib may obstruct the view of an internal organ.
A problem associated with all ultrasonic transducers is that during the scanning mode the face temperature of the transducer increases. The heating of the transducer face is directly related to the power supplied to the transducer elements located in the transducer face. It is desirable to supply sufficient power to the transducer elements because more power results in deeper penetration by the ultrasonic signals, yielding significantly clearer images.
The Federal Food and Drug Administration (FDA) has prescribed regulatory standards which limit the face temperature and the ultrasound intensity, i.e., power output of the transducer for product safety reasons, as well as to prevent unhealthy bioeffects. The present standard is that the face temperature of the transducer may not exceed 41.degree. C. The practical effect of the FDA standards is that the desired ultrasonic penetration cannot be reached because operation at the power limit would result in exceeding the allowable transducer face temperature. Under certain scanning mode conditions, the desired intensity limits cannot be reached because face heating is the first limiting parameter reached. Therefore, a method for cooling the ultrasonic transducer face is necessary so that the transducer can operate at optimum power levels for deeper penetration and clearer images.